The present invention relates to an electrophotographic copying machine and, more particularly, to a device for detecting the size of a copy document on a document table for an electrophotographic copying machine.
An electrophotographic copying machine produces an electrostatic latent image on an optical-sensitive member. The latent image corresponds to an image on a copy document such as a manuscript or book to be copied. Toner particles are electrically adhered to the latent image, so that the latent image becomes visible to form a toner image.
The toner image is transferred onto copy paper via a transference charger. Depending upon the size of the copy document, the size of the copy paper should be selected. To properly select the copy paper size, some sensors must be provided adjacent the document table for detecting the size of the copy document.
Conventionally, some pairs of sensors are provided each of which comprises a light emitting element and a light receiving element. The number of said sensors correspond to the number of the kinds of copy paper the sizes of the papers to be detected. The light emitting element is positioned at the document cover which is pivotably mounted on the document table. The light receiving element is positioned beneath a document table plate. When a specific size copy document is positioned on the document table and the document cover covers the copy document on the document table plate, the copy document interrupts light from the light emitting element to the light receiving element. By detecting the light receiving element which is prevented from receiving the light, the specific size of the copy document can be detected.
In the above conventional device, it is difficult to detect the specific size of the copy document when the copy document is fairly transparent, so that the S/N ratio of the light receiving element is too poor to correctly detect the particular size of the copy document. Further, the light emitting element must be positioned on the document cover, so that careful consideration should be taken for problems in wiring the element and the document cover which must be pivotably activated. The document cover must be closed to cover the copy document on the document table.
Otherwise, only some light receiving elements are positioned beneath the document table cover. When the copy document is positioned on the document table plate, the copy document interrupts the surrounding light from being incident upon the light receiving element. The copying machine is responsive to the output from the light receiving element for detecting the size of the copy document.
Since each of these elements is directed to detect an individual size of a plurality of copy documents, error detection could not be avoided, in particular, when the copying machine is operated in the dark.
Therefore, it is desired to provide an improved detection device for detecting the sizes of the copy documents on the document table which prevents in detection.